Physiology, Laboratory Testing, and Iodine
4
TSH
TPOAb and TgAb
No (thyroidal) effects on fetus or newborn
TSHR-Ab
Depending on subtype, can stimulate or block
the fetal thyroid
Iodine
a
Necessary for fetal thyroid hormone
production
Radioactive iodine
Destruction of fetal thyroid gland
Propylthiouracil and methimazole
Inhibit fetal thyroid function
Propranolol
Considered safe, associated with slightly
lower birth weight
(Lio)triiodothyronine
(Levo)thyroxine
Regulates fetal growth and development
Mother
Placenta
Figure 2. Transplacental Passage of Thyroid Parameters
and Drugs
a
Iodine overload may also result in fetal/neonatal hypothyroidism.
Maternal TSHR-Ab, iodine, radioactive iodine, the antithyroid drugs (propylthiouracil and
methimazole), propanolol, and the thyroid hormones [(lio)thyronine and (levo)thyroxine] all traverse
the placenta and have the potential to induce direct effects to the fetus.
No placental passage Placental passage
but no effects on fetus
